:{
add :: Int -> Int -> Int
add a b = a + b
:}
add 2 3

-- override
add = sum
add [1,2,3]

:{
a 0 = 0
a x = 1 + b x
b x = 2 + a (x -  1)
:}
b 2

-- do not show warning twice
{-# foo #-}

:{
{-# WARNING Foo "Just a warning" #-}
data Foo = Foo String
:}

:seti -XStandaloneDeriving
deriving instance Show Foo

-- ^ Just a 'foo' function.
foo = Foo "Some foo"
show foo

import Data.Char

:seti -XDefaultSignatures
:{
class HasString a where
  update :: a -> (String -> String) -> a

  upcase :: a -> a
  upcase x = update x (fmap toUpper)

  content :: a -> String
  default content :: Show a => a -> String
  content = show
:}

:{
instance HasString Foo where
  update (Foo s) f = Foo (f s)
  content (Foo s) = s
:}

upcase foo

{-# RULES "map/map" forall f g xs. map f (map g xs) = map (f.g) xs #-}
{-# ANN foo (Just "Hello") #-}
{-# NOVECTORISE foo #-}

:seti -XRoleAnnotations
:{
type role T1 _ phantom
data T1 a b = MkT1 b
:}

:{
type role T2 _ nominal
data T2 a b = MkT2 a
:}